1. Field of the Invention
The present invention relates, in general, to a cooling device for halogen lamps in microwave ovens and, more particularly, to a cooling device designed to more effectively cool the halogen lamps in microwave ovens by installing an exhaust fan at a position around the air outlet part of an air passage behind the halogen lamps.
2. Description of the Prior Art
As well known to those skilled in the art, several types of electric cooking devices, designed to directly or indirectly utilize electric power while cooking, have been proposed and used. An example of conventional electric cooking devices is a microwave oven using a magnetron as a heat source. In such a microwave oven, the magnetron is electrically operated to generate microwaves and applies the microwaves to food in a cavity, thus allowing the microwaves to cause an active molecular motion in the food. Such an active molecular motion in the food generates molecular kinetic energy, thus heating and cooking the food. Such microwave ovens are advantageous in that they have a simple construction and are convenient to a user while cooking, and easily and simply heat food in the cavity. The microwave ovens are thus somewhat preferably used for some cooking applications, such as a thawing operation for frozen food or a heating operation for milk requiring to be heated to a desired temperature.
However, such microwave ovens also have the following problems. That is, the ovens have a defect in their heating style in addition to limited output power of the magnetron, and so it is almost impossible to freely or preferably use them for a variety of cooking applications, without limitation. In a detailed description, the conventional microwave ovens only utilize a magnetron as a heat source, thus undesirably having a single heating style. In addition, the output power of the magnetron, installed in such ovens, is limited to a predetermined level. Therefore, the conventional microwave ovens fail to provide a quick and highly effective cooking operation. During a cooking operation utilizing such a microwave oven, food in a cavity is heated at its internal and external portions at the same time, and this may be an advantage of the oven in some cases. However, such a heating style may result in a disadvantage while cooking some food.
In an effort to overcome the above-mentioned problems, several types of microwave ovens, having another heat source in addition to a magnetron, have been proposed and used. For example, a microwave oven, having a convection heater in addition to a magnetron in a casing and originally designed to be used for a variety of cooking applications, has been proposed. However, such a convection heater only acts as a single heat source, thus failing to allow the microwave oven to have a variety of operational functions.
In order to solve the problems of the conventional microwave ovens, another type of microwave oven, utilizing a light wave, has been proposed. In this microwave oven, a lamp, wherein at least 90% of the radiation energy has a wavelength of not longer than 1 .mu.m, is used as the additional heat source. In said microwave oven, both visible rays and infrared rays from the lamp are appropriately used, and it is possible to preferably heat the exterior and interior of food while making the most of characteristics of the food. An example of such a lamp is a halogen lamp.
Due to a difference in wavelengths between the infrared rays and visible rays emanating from a halogen lamp, the heating styles for the exterior and interior of food are different from each other. While cooking pizza utilizing a halogen lamp, it is possible to appropriately heat the pizza in a way such that the exterior of the pizza is heated to become crisp and the interior is heated to be soft while maintaining appropriate moisture.
FIG. 1 is a conventional microwave oven utilizing a halogen lamp as an additional heat source. As shown in the drawing, the microwave oven comprises two halogen lamps 12 and 14 installed on the top wall 10 of a cavity 2. The microwave oven uses the light waves, radiated from the lamps 12 and 14, for heating food in the same manner as that described above, with the characteristics of the light waves remaining the same as that described above.
A light reflection plate 16 is installed at a position above the halogen lamps 12 and 14, thus reflecting any light waves, emanating upwardly from the lamps 12 and 14, back downwardly into the cavity 2. A plurality of light transmitting holes 18 are formed on the top wall 10 of the cavity 2, with the halogen lamps 12 and 14 being held on the top wall.
The halogen lamps 12 and 14 generate a large amount of light waves during an operation of the microwave oven, and so the lamps 12 and 14 are heated to a high temperature and may be undesirably overheated. Therefore, it is necessary to completely cool the halogen lamps 12 and 14. In order to accomplish the above object, the microwave oven is provided with a cooling device as shown in FIG. 2.
As shown in the drawing, the typical cooling device comprises a cooling fan unit 20 provided at a position around the lamps 12 and 14. In the cooling device, the cooling air current, generated from the cooling fan unit 20, passes through an air guide duct 22 while flowing along the halogen lamps 12 and 14 prior to being discharged from the duct 22 into the atmosphere as shown by the arrows in FIG. 2.
The above guide duct 22 has the following structure. That is, the guide duct 22 extends in the same direction as the axis of the lamps 12 and 14. The duct 22 is, thereafter, bent at an angle of 90.degree. at a position around the left-side end of the lamps 12 and 14 in FIG. 2. The outlet end of the duct is thus open to the front of the microwave oven. Due to such a structure of the duct 22, the cooling air current, emanating from the fan unit 20, flows along the lamps 12 and 14 while cooling them. The air current is, thereafter, discharged from the duct 22 into the atmosphere through the outlet end of the duct 22.
However, the above cooling device is problematic as follows. That is, the duct 22 is bent at an angle of 90.degree. at the position around the left-side end of the lamps 12 and 14 in FIG. 2 as described above. Therefore, the duct 22 forms a vortex of the air current at its bent portion and causes an excessive energy loss of the air current at that portion. This prevents the air current from being smoothly discharged from the duct into the atmosphere.